The present invention relates to a method of making silicone foam having reduced density and to silicone foam compositions used in such method. More particularly, the present invention relates to the use of a hydride polysiloxane in the form of a mixture of a linear hydride polysiloxane and a cyclic hydride polysiloxane to effect a significant reduction in foam density of silicone foam resulting from the platinum catalyzed reaction between a vinyl-terminated polydiorganosiloxane, a hydride polysiloxane, and a hydroxylated material, which are defined more particularly hereinafter.
Elastomeric silicone foams have been used in a variety of applications such as thermo- and electrical insulators, foam barriers, and cushions. Even though elastomeric silicone foams are superior to organic foams in many instances, organic foams are often used based on economic consideration.
At the present time, commercially available silicone foam has a foam density which can provide a 15-25 pound/cubic ft. foam structure. One method of reducing the cost of elastomeric silicone foam, is to reduce foam density without altering the desirable physical properties of the foam material.
Although silicone foam may be made by using a blowing agent, or even mechanical mixing, another technique is by effecting the generation of hydrogen gas using a platinum catalyst as shown by Smith, U.S. Pat. No. 3,923,705. Elastomeric silicone foams can be made by forming a mixture of a silanol, a silicone hydride, and a vinyl-containing silicone in the presence of a platinum catalyst. There is effected the simultaneous generation of hydrogen gas along with cross-linking. For example, Modic, U.S. Pat. No. 4,189,545 produces silicone foam by adding water to a composition of a vinyl-containing siloxane, a hydride-containing siloxane and platinum to generate hydrogen simultaneously with cross-linking. Modic, U.S. Pat. No. 4,418,157 shows the strengthening of silicone foam by adding a resinous copolymer, while Bauman et al., U.S. Pat. No. 4,599,367 reduces silicone foam density by using a combination of silanol and water.
The present invention is based on the discovery that a substantial reduction in silicone foam density can be achieved by using a hydride polysiloxane in a silicone foamable mixture comprising a vinyl-terminated polydiorganosiloxane, a hydride polysiloxane, a hydroxylated material and an effective amount of a platinum catalyst, where the hydride polysiloxane in such silicone foamable mixture consists essentially of a mixture of a linear hydride polysiloxane, and a cyclic hydride polysiloxane. A further reduction in silicone foam density can be achieved by using an aqueous mixture of a C.sub.(1-8) alkanol, such as a mixture of water and methanol.